JP6862702B2 - Zirconia calcined body and its manufacturing method - Google Patents

Description

The present invention relates to a zirconia calcined product as a raw material for a zirconia sintered body and a method for producing the same.

Since the zirconia sintered body has very high strength, it is difficult to directly process it to process its shape. Therefore, as a method for producing a zirconia sintered body having a complicated shape, a zirconia powder is formed and then fired at a temperature lower than the sintering temperature to obtain a calcined body, which is machined and then sintered. , There is a way to obtain a zirconia sintered body.

For example, Patent Document 1 describes that a zirconia molded product obtained by molding a powder having a linear shrinkage rate of 0.2 to 1.0% from a molded product to a calcined product in a firing process is fired at 800 to 950 ° C. By doing so, the calcined body obtained for the purpose of improving the variation in the shrinkage rate is disclosed. It is disclosed that the calcined body is further processed into the shape of a dental material by CAD / CAM and then sintered to obtain a zirconia sintered body for a dental material.

It is considered that there is some effect on obtaining the zirconia sintered body having the target shape by suppressing the variation in the shrinkage rate at the time of sintering the machined calcined body. However, since chipping, cracking, etc. actually occur during machining before tooth sintering, the method of Patent Document 1 is an essential solution for faithfully reproducing the shape of the designed calcined body. It doesn't become. In addition to this, Patent Document 1 does not disclose the method itself for controlling the linear shrinkage rate, so that it is not possible to realistically suppress the variation in the shrinkage rate.

Further, in Patent Document 2, in order to facilitate cutting, a zirconia calcined product obtained by degreasing and calcining zirconia powder coated with an acrylic resin in a hydrogen-containing nitrogen atmosphere is made workable. It is disclosed that it is excellent.

JP-A-2010-220779 JP 2013-119485

The method of Patent Document 1 cannot improve the processability of the calcined body, and the calcined body of Patent Document 2 requires degreasing and calcining under a special condition of a hydrogen-containing nitrogen atmosphere. Therefore, it is difficult to apply it as an industrial manufacturing method premised on mass production.

An object of the present invention is to provide a calcined body which can be expected to have better machinability as compared with a conventional calcined body, and an industrially applicable manufacturing method of such a calcined body.

The present inventor examined the processability of the calcined body. As a result, they found that the microstructure of the calcined body was different from that of the conventional calcined body, and found that it could be expected that chipping, cracking, etc. during machining would be less likely to occur.

That is, the present invention is a zirconia calcined product having a content ratio of particles having a maximum diameter of 1 μm or more of 15 particles / μm ² or less and a density of 2.8 g / cm ³ or more and 3.6 g / cm ^{3 or less.} ..

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a calcined body that can be expected to have better machinability as compared with a conventional calcined body, and an industrially applicable manufacturing method of such a calcined body.

Electron microscope observation diagram of Example 1 (a) Magnification: 2500 times, scale in the figure is 10 μm (b) Magnification: 30,000 times, scale in the figure is 100 nm Electron microscope observation diagram of Example 2 (a) Magnification: 2500 times, scale in the figure is 10 μm (b) Magnification: 30,000 times, scale in the figure is 100 nm Electron microscope observation diagram of Comparative Example 1 (a) Magnification: 2500 times, scale in the figure is 10 μm (b) Magnification: 30,000 times, scale in the figure is 100 nm Electron microscope observation diagram of Comparative Example 2 (a) Magnification: 2500 times, scale in the figure is 10 μm (b) Magnification: 30,000 times, scale in the figure is 100 nm Electron microscope observation diagram of Comparative Example 3 (a) Magnification: 2500 times, scale in the figure is 10 μm (b) Magnification: 30,000 times, scale in the figure is 100 nm

The terms used herein are as follows.

A "sol particle" is an independent particle composed of sol crystals of hydrated zirconia sol. Further, the "sol crystallite" is a particle having the smallest unit composed of regularly arranged zirconia, and is a particle constituting the zirconia sol particle.

The "zirconia powder" is a powder obtained by heat-treating a hydrated zirconia sol, and is composed of at least one of secondary particles or primary particles of zirconia. Further, the "secondary particles" are aggregated particles in which the primary particles of zirconia are aggregated. Examples of secondary particles include granules. A "primary particle" is an independent particle composed of zirconia crystallites. Further, the "zirconia crystallite" is a particle having the smallest unit composed of regularly arranged zirconia, and is a particle constituting a primary particle.

The "zirconia molded product" is one in which zirconia powder is aggregated by compression or the like and has a certain shape.

The "zirconia calcined body" is zirconia in a state where it has undergone the initial sintering stage, and has a structure in which zirconia particles form an interface with each other, that is, a structure in which so-called zirconia particles are necked. For example, a zirconia molded product obtained by heat-treating the zirconia molded product in the air at 1150 ° C. or lower can be mentioned.

The "zirconia sintered body" is zirconia in a state where it has passed through the middle stage and the late stage of sintering, and is composed of crystal particles and has been densified.

In the present invention, the "average particle diameter determined from BET specific surface area (hereinafter, also referred to as" _{D B} ".)" Are according to JIS R1626-1996, and the BET method 1-point method adsorbates nitrogen _{(N 2)} It is a value obtained from the following formula from the BET specific surface area of the zirconia powder obtained by.
_{D B = 6000 / (S ·} ρ)
In the above formula, _{D B} average particle diameter is determined from the BET specific surface area (nm), S is the BET specific surface area ^(m 2 / g), and, [rho is the theoretical density (g / cm ^3).

Further, ρ can be obtained from the following equation.
_{ρ = 5.8 × f m /100+6.1×(100-f m} ) / 100
In the above formula, [rho theoretical density (g / ^cm 3), and, is _{f m} is a percentage of monoclinic crystals (%) which is obtained from the equation described below.

The "average particle size measured by an electron microscope (hereinafter, _{also referred to as" DT} ")" in the present invention is a random number of 100 or more independent minimum unit particles in an electron microscope observation diagram of zirconia powder. It is an average value of the particle diameters obtained by extracting and converting the area of the particles into a circle.

The "monoclinic crystal ratio" in the present invention is the ratio of monoclinic zirconia contained in the crystal phase of the zirconia powder, and is a value obtained by the following formula for the powder X-ray diffraction pattern of the zirconia powder.

_{f m = [I m (111} ) + I m (11-1)] × 100
_{/ [I m (111) +} I m (11-1) + I t (111)]

In the above formula, _{f m} is percentage of monoclinic crystals _(%), I m (111) is the area strength of the XRD peak corresponding to the (111) plane of monoclinic _zirconia, I m (11-1) monoclinic area intensity of the XRD peak corresponding to the (11-1) plane of the zirconia, _and, I t (111) is the area strength of the XRD peak corresponding to the (111) plane of tetragonal zirconia.

In the present invention, "crushing" is a process of applying an external force to the zirconia powder to disperse the primary particles, and "crushing" is a monoclinic crystal of the zirconia powder after crushing with respect to the zirconia powder before crushing. Examples thereof include pulverization in which the rate of increase (hereinafter, also referred to as “monoclinic crystal increase rate”) is 5% or less. On the other hand, "mechanical pulverization" is pulverization in which the rate of increase of monoclinic crystals exceeds 5%.

Hereinafter, the zirconia calcined body of the present invention will be described.

The calcined product of the present invention has a maximum diameter of 1 μm or more and a particle content ratio of 15 particles / μm ² or less. Particles with a maximum diameter of 1 μm or more (hereinafter, also referred to as “coarse sintered particles”) are particles with denser aggregation than other particles in the calcined body, and the sintering has progressed relatively excessively. It is thought that it is formed in. It is preferable that the coarse sintered particles do not exist on either the surface or the inside of the calcined body, but the coarse sintered particles existing on the surface of the calcined body can be removed by a simple surface treatment. On the other hand, the coarse sintered particles existing inside the calcined body are often confirmed to exist only when they are processed into a desired shape, and it is difficult to remove them prior to machining. Therefore, the ratio of the coarse sintered particles in the calcined body of the present invention is preferably the ratio of the coarse sintered particles inside the calcined body, which is observed in the electron microscope observation view of the cross section of the calcined body. It can be obtained as the ratio of coarse sintered particles.

Coarse sintered particles, especially the coarse sintered particles existing inside the calcined body, cause non-uniform shrinkage when the calcined body is sintered and hinder densification, resulting in zirconia firing of the desired shape. It becomes difficult to obtain a body. In addition to this, it can also be a source of defects during processing such as chipping. It is preferable coarse crystal grains is small, the proportion of coarse sintered particles 10 / [mu] m ² or less, more preferably 5 / [mu] m ² or less, particularly preferably 1 / [mu] m ² or less. The content ratio of the coarse sintered particles may be determined from an observation diagram measured by a scanning electron microscope (hereinafter referred to as “SEM”) of a cross section of the calcined body. Specifically, the calcined body is subjected to focused ion beam processing to obtain a cross section of the calcined body, and the number of coarse sintered particles per unit area of the calcined body cross section in the SEM observation diagram of the cross section (pieces / μm ^2). ) May be the content ratio of the coarse sintered particles. In this case, the SEM observation map may be observed in a field of view having a length of 30 to 50 μm and a width of 50 to 30 μm, and an SEM observation map having three or more visual fields may be used.

Further, the coarse sintered particles are particles having a maximum diameter of 1 μm or more, and in the case of particles having a high aspect ratio, the length of the major axis is measured, and those having a major axis of 1 μm or more are regarded as coarse sintered particles. Good. Since the calcined product of the present invention is preferably composed of more uniform zirconia particles, the coarse sintered particles are preferably particles having a maximum diameter of 0.7 μm or more, and particles having a maximum diameter of 0.5 μm or more. Is even more preferable.

Since the calcined product of the present invention is a zirconia molded product that has undergone the initial stage of sintering, the zirconia powder in the molded product is in a state of being necked. Therefore, the average particle size of the zirconia particles of the calcined product of the present invention _{tends to be about the same as the average particle size (DT} ) of the zirconia powder used as a raw material, and is 70 nm or more and 400 nm or less, further 100 nm or more and 300 nm or less, and further. Is 100 nm or more and 250 nm or less.

Calcined body of the present invention has a density of 2.5 g / cm ³ or more 3.6 g / cm ³ or less, more or less at 2.5 g / cm ³ or more 3.3 g / cm ^3. If the density is ^{less than 2.5 g / cm 3} , the shape becomes fragile during processing. On the other hand, when ^{it exceeds 3.6 g / cm 3} , the calcined product tends to contain coarse agglomerated particles in which the sintering has progressed too much. Coarse agglomerated particles cause chipping and scratches during processing. More preferable densities include 2.7 g / cm ³ or more and 3.0 g / cm ³ or less.

The density of the caliper may be determined as the weight of the caliper relative to the volume of the caliper measured using a caliper or the like.

The calcined product of the present invention may have the above physical characteristics, but it is preferably zirconia containing 2 mol% or more and 6 mol% of yttria. The yttria content is preferably 2 mol% or more and 4 mol% or less, and more preferably 2.5 mol% or more and 3.5 mol% or less. As a result, the zirconia calcined product of the present invention becomes a crystal phase having tetragonal crystals as the main phase.

In the present invention, the yttria content is the molar ratio of yttria to the total _{of zirconia (ZrO 2} ) and yttria (Y ₂ O _{3) in the calcined product.}

The calcined product of the present invention _{may contain alumina (Al 2} O ₃ ), and the alumina content is 0% by weight or more and 0.3% by weight or less, and further 0% by weight or more and 0.25% by weight or less. All you need is. The inclusion of alumina facilitates sintering at lower temperatures. When the zirconia calcined product of the present invention contains alumina, the alumina content is preferably 0.01% by weight or more and 0.3% by weight or less, and more preferably 0.01% by weight or more and 0.25% by weight or less. ..

In the present invention, the yttria content is the weight ratio of alumina to the total _{of zirconia (ZrO 2} ), yttria (Y ₂ O ₃ ) and alumina (Al ₂ O _{3) in the zirconia powder.}

Hereinafter, the method for producing the zirconia calcined product of the present invention will be specifically described.

The zirconia calcined product of the present invention has a molding step of molding a zirconia powder in which the ratio of the particle size determined by electron microscope observation to the particle size determined from the BET specific surface area is 2.2 or more and 4.0 or less. It can be obtained by a production method having a firing step of firing the obtained molded product at 800 ° C. or higher and 1100 ° C. or lower.

In the molding step, zirconia powder in which the ratio of the particle size determined by electron microscope observation to the particle size determined from the BET specific surface area is 2.2 or more and 4.0 or less is formed. As a result, a molded product to be used in the firing step can be obtained.

The zirconia powder used in the molding step has a ratio of _{DT to D B (hereinafter, also referred to as “DT} / D _B ratio”) of 2.2 or more and 4.0 or less. _{Both DB} and _DT are indicators of the primary particle size. D _B is the value that reflects the state of the zirconia crystallites, whereas, D _T is the value of the apparent not reflect the state of the zirconia crystallites. The zirconia powder having a D _T / D _B ratio outside the range of the present invention is a powder in which particle aggregation is excessively advanced due to partial sintering of primary particles, so-called necking, or a physics in which the primary particles are strong. It becomes a cohesive powder that is agglomerated by a certain force. When a zirconia sintered body is obtained using such a zirconia powder, it is necessary to disperse the primary particles by mechanical pulverization. However, mechanical pulverization produces a large amount of monoclinic crystals in the zirconia powder, so that the zirconia powder has reduced sinterability. On the other hand, _{by satisfying the above DT} / D _B ratio, mechanical pulverization is not required. As a result, the zirconia powder used in the molding step becomes a zirconia powder in which the sinterability is not deteriorated due to the large amount of monoclinic crystals. 2.3 to 3.5 as a preferred _D T / _{D B} ratio, more can be mentioned 2.3 to 3.0.

Zirconia powder to be subjected to forming process, while satisfying the _D T / _{D B} ratio of the, _{D T} is 70nm or 400nm or less, and more preferably 100nm or more 300nm or less, or even is 100nm or more 250nm or less. When _DT satisfies the above range, the powder has an appropriate sintering rate. By satisfying such a _DT and _DT / D _B ratio, it is possible to have high moldability and to increase the density in sintering at a lower temperature.

Zirconia powder to be subjected to forming process, meets _D T / _{D B} ratio of above yet, BET specific surface area of ^{6 m} 2 / g or more ^{20 m} 2 / g or less, and further is ^9m 2 / g or more ^{20 m} 2 / g or less Is preferable. When the BET specific surface area is 20 m ² / g or less, agglutination of primary particles is suppressed, and the powder tends to have excellent operability (handling). On the other hand, when the BET specific surface area is 6 m ² / g or more, the powder has an appropriate sinterability. From the viewpoint of combining sinterability and moldability, the BET specific surface area is preferably 10 m ² / g or more and 20 m ² / g or less, and ^{more preferably 11 m 2} / g or more and 19 m ² / g or less.

Zirconia powder to be subjected to molding process, _D T / _{D B} ratio described above, furthermore, satisfy the above-mentioned _D T / _{D B} ratio and _{D T,} may be any / _{D B.} Preferred 50nm or 170nm or less as _{D B,} even 50nm or 110nm or less, or even 50nm or 100nm or less, or even can be exemplified 50nm or 90nm or less.

Zirconia powder to be subjected to forming process, the particle size of the zirconia crystallites is determined by the following formula (hereinafter, also referred to as "crystallite diameter" or _{"D X".)} Is, 15 nm or more 40nm or less, even 18nm or 35nm or less Is preferable.

D _X = κλ / (βcosθ)
In the above formula, Dx is the crystallite diameter (nm) of the zirconia crystallite, κ is the Scheller constant (1), λ is the wavelength (nm) of the light source for powder X-ray diffraction measurement, and β is the diffraction depending on the X-ray diffractometer. The half-value width (°) after correcting the spread of the line width and θ are the black angles (°) of the reflection corresponding to the (111) plane of the square zirconia in the powder X-ray diffraction measurement. When CuKα ray is used as a light source for powder X-ray diffraction measurement, λ is 0.15405 nm.

Since the zirconia powder used in the molding process has almost no necking, mechanical grinding is not required. The monoclinic crystal ratio of the zirconia powder of the present invention is 10% or less, further 8% or less, and further 4% or less, and the primary particles have very few monoclinic crystals as compared with the conventional zirconia powder. It becomes a dispersed powder.

The zirconia powder of the present invention preferably contains 2 mol% or more and 6 mol% yttria. The yttria content is preferably 2 mol% or more and 4 mol% or less, and more preferably 2.5 mol% or more and 3.5 mol% or less. As a result, the zirconia powder of the present invention becomes a crystal phase having tetragonal crystals as the main phase.

In the present invention, the yttria content is the molar ratio of yttria to the total _{of zirconia (ZrO 2} ) and yttria (Y ₂ O _{3) in the zirconia powder.}

The zirconia powder used in the molding step _{may contain alumina (Al 2} O ₃ ), and the alumina content is 0% by weight or more and 0.3% by weight or less, and further 0% by weight or more and 0.25% by weight or less. All you need is. The inclusion of alumina facilitates sintering at lower temperatures. When the zirconia powder of the present invention contains alumina, the alumina content is preferably 0.01% by weight or more and 0.3% by weight or less, and more preferably 0.01% by weight or more and 0.25% by weight or less.

In the present invention, the yttria content is the weight ratio of alumina to the total _{of zirconia (ZrO 2} ), yttria (Y ₂ O ₃ ) and alumina (Al ₂ O _{3) in the zirconia powder.}

Zirconia powder to be subjected to molding process, can be produced by any method as long as the D _{T /} D _B ratio described above, as a preferred method, an average sol particle size by hydrolyzing a zirconium salt aqueous solution A hydrolysis step for obtaining a hydrated zirconia sol aqueous solution containing a hydrated zirconia sol having a concentration of 150 nm or more and 400 nm or less, a cleaning step for adjusting the unreacted zirconium content in the hydrated zirconia sol aqueous solution to 1% or less, and a cleaning step. A production method including a heat treatment or baking step of the subsequent hydrated zirconia at 850 ° C. or higher and 1200 ° C. or lower can be mentioned.

In the hydrolysis step, the zirconium salt aqueous solution is hydrolyzed. As a result, hydrated zirconia sol is produced from the zirconium salt, and an aqueous solution of hydrated zirconia sol is obtained.

Examples of the zirconium salt contained in the zirconium salt aqueous solution include at least one of the group consisting of zirconium oxychloride, zirconium nitrate, zirconium chloride and zirconium sulfate, and zirconium oxychloride.

The hydrated zirconia sol obtained in the hydrolysis step has an average sol particle size of 150 nm or more and 400 nm or less. When the average sol particle size is in the range, the D _T / D _B ratio of the zirconia powder obtained after calcination is within the range of the zirconia powder of the present invention. The average sol particle size of the hydrated zirconia sol is preferably 180 nm or more and 400 nm or less, and more preferably 180 nm or more and 300 nm or less.

If a hydrated zirconia sol having the above average sol particle size is obtained, the hydrolysis method is arbitrary, but it can be hydrolyzed by boiling and refluxing an aqueous zirconium salt solution. The hydrolysis may be carried out as long as the zirconium salt proceeds sufficiently, and examples thereof include 130 hours or more and 200 hours or less.

Further, by hydrolyzing the anion concentration in the zirconium salt aqueous solution to 0.2 mol / L or more and 0.6 mol / L or less, and further 0.3 mol / L or more and 0.5 mol / L or less, the average sol particle size is increased. A hydrolyzed zirconia sol having a diameter of 150 nm or more and 400 nm or less can be efficiently obtained.

The hydrated zirconia sol aqueous solution obtained in the hydrolysis step is an aqueous solution containing unreacted zirconium in addition to the hydrated zirconia sol. In the washing step, the unreacted zirconium content in the aqueous solution is set to 1% by weight or less, further 0.5% by weight or less, and further 0.1% by weight or less. When the unreacted zirconium content of the hydrated zirconia sol aqueous solution exceeds 1% by weight, sintering between the primary particles is promoted in the calcination step, so that the powder tends to have low sinterability.

In the washing step, if the unreacted zirconium content is 1% by weight or less, the hydrated zirconia sol aqueous solution may be washed by any washing method. Examples of the cleaning method include cleaning the hydrated zirconia sol aqueous solution obtained in the hydrolysis step with a sufficient amount of pure water. As a preferable cleaning method, ultrafiltration can be mentioned, and further, filtration using an ultrafiltration membrane having a molecular weight cut-off of 5 to 3 million can be mentioned.

The unreacted zirconium is zirconium contained in the aqueous solution of hydrated zirconia sol and exists in addition to the hydrated zirconium sol, and examples thereof include unhydrolyzed zirconium salts. Further, the unreacted zirconium content can be calculated by the following formula.

α = m / m ₀ × 100
In the above formula, the α unreacted zirconium content (wt%), m is the content of unreacted zirconium (mg), and, m _o zirconia content of the hydrated zirconia sol solution (mg). m is the weight obtained by converting the zirconium concentration in the filtrate after washing measured by inductively coupled plasma emission spectroscopy into zirconia (ZrO _{2 ), and m 0} is the hydrated zirconia sol aqueous solution after washing at 1000 ° C. or higher. It is the weight of the solid content obtained after heat treatment at 1200 ° C. or lower for 1 hour.

In the production method of the present invention, it is preferable to have an yttria mixing step of mixing hydrated zirconia and an yttria source between the washing step and the baking step. As a result, the obtained zirconia powder can be made into a zirconia powder containing a desired amount of yttria.

The amount of the yttria source added is such that the yttria concentration of the obtained hydrated zirconia is 2 mol% or more and 6 mol%, further 2 mol% or more and 4 mol% or less, and further 2.5 mol% or more and 3.5 mol% or less. It may be mixed with zirconia.

The yttria concentration is the molar ratio of yttria to the total amount of zirconia and yttria in hydrated zirconia.

The yttria source is yttria (Y ₂ O ₃ ) or an yttrium compound that is a precursor thereof, and at least one of the group consisting of yttrium chloride, yttrium nitrate and yttrium oxide, and at least one of yttrium chloride or yttrium oxide. Can be mentioned.

The mixing method when mixing the hydrated zirconia and the yttria source is arbitrary. The yttria source may be mixed with the hydrated zirconia sol aqueous solution after the washing step (hereinafter, also referred to as “liquid phase mixing”), or the hydrated zirconia sol aqueous solution after washing may be obtained by solid-liquid separation and drying. The yttria source may be mixed with the hydrated zirconia powder (hereinafter, also referred to as “solid phase mixing”).

In the case of liquid phase mixing, the yttrium source may be mixed with the hydrated zirconia sol aqueous solution by any method. Since zirconia and yttria become more uniform, it is preferable to mix the yttria source with the hydrated zirconia sol aqueous solution and then mix the alkaline source to co-precipitate the yttria-containing zirconia. The yttria-containing zirconia obtained as a coprecipitate may be solid-liquid separated and dried by any method. In the case of liquid phase mixing, the yttrium source is preferably at least one of yttrium chloride and yttrium nitrate, and in the case of coprecipitation, the alkali source is at least one of the group consisting of ammonia, sodium hydroxide and potassium hydroxide. Is preferable.

In the case of solid phase mixing, first, a hydrated zirconia sol aqueous solution is solid-liquid separated and dried by an arbitrary method to obtain a hydrated zirconia powder. The yttria source may be mixed with the obtained hydrated zirconia powder.

Drying in liquid phase mixing and solid phase mixing may be carried out in the air at 100 ° C. or higher and 250 ° C. or lower.

In the calcination step, heat treatment is performed at 850 ° C. or higher and 1200 ° C. or lower. As a result, the zirconia powder of the present invention can be obtained. If the calcination is less than 850 ° C., the zirconia crystallites become too small, resulting in a zirconia powder having low sinterability. Such zirconia powder has a low density of the sintered body obtained even if it is sintered at a low temperature. On the other hand, if heat treatment is performed at a temperature exceeding 1200 ° C., necking tends to proceed, and the powder does not disperse unless it is mechanically pulverized.

Preferred heat treatment conditions include 870 ° C. or higher and 1050 ° C. or lower in the atmosphere.

The production method of the present invention may include at least one of an alumina mixing step, a crushing step, and a granulation step, if necessary.

In the alumina mixing step, the aqueous solution of hydrated zirconia sol and hydrated zirconia so that the alumina content is 0.01% by weight or more and 0.3% by weight or less, and further 0.01% by weight or more and 0.25% by weight or less. The powder or zirconia powder is mixed with an alumina source. As a result, the alumina-containing zirconia powder can be obtained.

The alumina mixing step may be performed at any stage after the cleaning step, preferably at least after the washing step or after the calcination step, and may be performed at the same time as the yttria mixing step. It is preferable to have an alumina mixing step after the cleaning step in order to disperse the alumina more uniformly and not to apply a load due to mixing to the zirconia powder.

The alumina source may be alumina (Al ₂ O ₃ ) or a precursor thereof, and is preferably at least one of the group consisting of aluminum hydroxide, alumina, aluminum nitrate and aluminum chloride, and is preferably alumina or an alumina sol. It is preferable to have.

The crushing step can remove the slow agglomeration of the zirconia powder after the calcination step. The crushing method is preferably performed so that the zirconia powder is not loaded more than necessary. In mechanical pulverization in which the rate of increase of monoclinic crystals exceeds 5%, pulverization causes destruction of primary particles. Since the zirconia powder obtained by the production method of the present invention does not have necking, it is preferable not to perform mechanical pulverization that causes destruction of primary particles.

In the granulation step, zirconia powder and a binder are mixed and granulated. This further improves the operability of the zirconia powder. Granulation may be carried out by any method, but it is preferable to mix the zirconia powder and the solvent to obtain a slurry, which is then spray-granulated. In this case, the zirconia powder may be dispersed in at least one of water and alcohol as a solvent, and further in water. As the granulated zirconia powder (hereinafter, also referred to as "zirconia granules"), the average granules are 30 μm or more and 80 μm or less, further 50 μm or more and 60 μm or less, and the bulk density is 1.00 g / cm ³ or more 1 .40g / cm ³ or less, and that further is 1.10 g / cm ³ or more 1.30 g / cm ³ or less.

In the molding step in the production method of the present invention, the zirconia powder as described above is molded to obtain a zirconia molded product (hereinafter, also simply referred to as “molded product”). The method is optional as long as the zirconia powder can be molded to agglomerate into the desired shape. Examples of the molding method include at least one molding method in the group consisting of press molding, cold hydrostatic press, casting molding, sheet molding and injection molding.

The molded product obtained in the molding step may be in a state in which the zirconia powder is aggregated so as to maintain a constant shape, and examples thereof include a relative density of 40% or more and 60% or less. The shape of the zirconia molded body is arbitrary, and at least one of a group consisting of a spherical shape, a substantially spherical shape, a substantially cylindrical shape, a disk, a substantially disk, a cube, a rectangular parallelepiped, and a polygon can be mentioned. The shape of the molded body has a great influence on the shape of the zirconia calcined body (hereinafter, also simply referred to as “temporary calcined body”) obtained in the subsequent firing step. In order to obtain a calcined body suitable for CAD / CAM processing, the molded body is preferably either a disk shape or a columnar shape.

In the firing step, the molded product obtained in the molding step is fired at 800 ° C. or higher and 1000 ° C. or lower. As a result, the zirconia calcined product of the present invention can be obtained.

The firing conditions in the firing step may be any conditions as long as a structure is obtained in which the zirconia particles in the molded body form an interface. There are three stages of zirconia sintering: early, middle and late. In the early stage of sintering, zirconia particles form an interface, and in the middle stage of sintering, the growth of the interface progresses and the zirconia particles bond with each other to grow crystal particles. Elimination of pores progresses at the same time, and densification progresses. Therefore, the firing conditions may be any heat treatment such that the zirconia molded product undergoes the initial sintering stage.

The sintering stage is mainly affected by temperature. Therefore, in the firing step, firing may be performed at 800 ° C. or higher and 1100 ° C. or lower, and further at 850 ° C. or higher and 1000 ° C. or lower. The firing atmosphere may be an oxidizing atmosphere, a reducing atmosphere, an inert atmosphere, or a vacuum atmosphere, but an oxidizing atmosphere is preferable, and since it is simple, it is more preferable to use an atmospheric atmosphere.

As for the firing time in the firing step, it is sufficient that the necking does not proceed sufficiently and the growth of the crystal particles does not proceed too much. For example, at the above temperature, 1 hour or more and 5 hours or less can be mentioned.

The firing method may be either normal pressure sintering or pressure sintering. Since it is not necessary to obtain a dense sintered body in the firing step, the firing method may be normal pressure sintering or atmospheric pressure sintering.

The microstructure of the calcined body of the present invention is very uniform. Therefore, even when this is processed, chipping and defects are unlikely to occur, and it can be processed into a desired shape.

Further, the calcined product of the present invention can be used to produce a zirconia sintered body regardless of whether or not it is processed. That is, a zirconia sintered body having a desired shape can be obtained by subjecting the calcined body of the present invention to mid-term and late-stage sintering.

As a method for producing a zirconia sintered body using the calcined product of the present invention, it can be mentioned that the calcined product of the present invention is sintered at atmospheric pressure at 1200 ° C. or higher and lower than 1600 ° C. in the air.

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to these examples.
(Measurement of average sol particle size)
The average sol particle size of the hydrated zirconia sol was measured using a dynamic light scattering type particle size distribution measuring device. As the pretreatment conditions for the sample, the hydrated zirconia sol-containing solution was suspended in pure water and dispersed for 3 minutes using an ultrasonic homogenizer.
(Measurement of monoclinic crystal ratio)
The XRD pattern of the powder sample was obtained by powder X-ray diffraction measurement. The monoclinic crystal ratio was determined from the obtained XRD pattern. A general X-ray diffractometer (trade name: Model RINT Ultimate III, manufactured by Rigaku Co., Ltd.) was used for the measurement. The conditions for powder X-ray diffraction measurement are as follows.
Radioactive source: CuKα ray (λ = 0.15418 nm)
Measurement mode: Continuous scan
Scan speed: 1 ° / min
Step width: 0.02 °
Divergence slit: 0.5 deg
Scattering slit: 0.5 deg
Light receiving slit: 0.3 mm
Measurement range: 2θ = 26 ° to 33 °

(Measurement of _DT)
From the observation drawings obtained using a transmission electron microscope, 300 particles were randomly extracted. _{The DT} of the zirconia powder was determined by analyzing the extracted particles with image analysis software (trade name: ImageJ).

(Measurement of _{D B)}
Using nitrogen as the adsorbed gas, the BET specific surface area of the powder sample was measured with a fluidized specific surface area automatic measuring device (device name: Flowsorb III2305, manufactured by Shimadzu Corporation). Prior to measuring the BET specific surface area, the powder sample was degassed at 250 ° C. for 30 minutes. By the following equation from the obtained BET specific surface area was determined D _B powder samples.
_{D B = 6000 / (S ·} ρ)
_{ρ = 5.8 × f m /100+6.1×(100-f m} ) / 100
In the above formula, the average particle _{diameter D B} is determined from the BET specific surface area (nm), S is the BET specific surface area ^(m 2 / g), ^ρ is the theoretical density (g / cm ³⁾ and _{f m} is percentage of monoclinic crystals (%).
(Measurement of bulk density)
The bulk density of the zirconia granules was determined by a constant volume measuring method according to JIS R1628.
(Measurement of average granule diameter)
The average granule diameter of the zirconia granules was determined by a mechanical sieving method according to JIS 1639-1.
(Measurement of content ratio of coarse sintered particles)
The calcined body sample was cut using a focused ion beam processing device (device name: SMI3050, manufactured by Seiko Instruments Inc.). Using a field emission electron microscope (device name: JSM7600F, manufactured by JEOL Ltd.), the cross section exposed by cutting was observed by SEM to obtain an SEM observation image of three fields of view having an image size (47 μm × 36 μm). The number of coarse sintered particles having a maximum diameter of 1 μm or more existing in the range of the obtained SEM observation image is counted, and the number of coarse sintered particles (pieces / μm ² ) with respect to the total area of the three-field image is used for coarse baking. The content ratio of the blotting particles was determined.
(Measurement of density of molded and calcined products)
The densities of the molded body sample and the calcined body sample were determined by dividing the volume by the weight. The weight was measured with a balance, and the volume was calculated from the size of the molded product.
(Measurement of sintered body density)
The density of the zirconia sintered body was measured by the Archimedes method.

(Measurement of average crystal grain size)
The average crystal grain size of the crystal particles of the sintered body was calculated by a planimetric method using a field emission scanning electron microscope. Specifically, a circle is drawn on the microscope image so that the total of the number of particles n _c in the circle and the number of particles Ni applied to the circumference is at least 200, and the nc and Ni are obtained by the planimetric method. The average crystal grain size was determined. In the case where the number of particles N _i is less than 200, the total number of crystal grains (n c _{+ N i)} is to be at least 200, using a microscope image of a plurality of field, each similar circle The average grain size was determined by drawing and the planimetric method.
Prior to the measurement, the sintered body sample was mirror-polished and then subjected to a thermal etching treatment to prepare it as a pretreatment. In the mirror polishing, the surface of the sintered body was ground with a surface grinding machine, and then diamond abrasive grains having an average particle diameter of 9 μm, 6 μm, and 1 μm were sequentially used for polishing with a mirror polishing device.
(Measurement of total light transmittance)
For the total light transmittance, an ultraviolet-visible spectrophotometer (device name: V-650, manufactured by JASCO Corporation) was used to measure the total light transmittance at a wavelength of 600 nm. Prior to the measurement, the sintered body sample was subjected to the same pretreatment as the measurement of the average crystal grain size to obtain a disk-shaped sample having a thickness of 1.0 mm.
(Measurement of bending strength)
The bending strength was evaluated by a three-point bending test according to JIS R1601.
(Hot water treatment test)
In order to confirm the deterioration of the sintered body sample, the sintered body sample was immersed in hot water at 140 ° C. for 60 hours. Sintered body after the process is XRD measurement to determine the monoclinic of the sintered body Akiraritsu (f _m).

Example 1
An aqueous solution of zirconium oxychloride having a zirconium concentration of 0.4 mol / L and a chloride ion concentration of 0.4 mol / L is hydrolyzed at a boiling temperature for 140 hours while stirring in a flask equipped with a recirculator to obtain a hydrated zirconia sol aqueous solution. Obtained. The average sol particle size of the hydrated zirconia sol in the hydrated zirconia sol aqueous solution was 250 nm.

The obtained aqueous solution of hydrated zirconia sol was filtered using an ultrafiltration membrane (molecular weight cut off: 6000), and then washed with a sufficient amount of pure water. The unreacted zirconium content of the hydrated zirconia sol aqueous solution after washing was 0.01% by weight.

Ittrium hexahydrate chloride was added and mixed with the hydrated zirconia sol aqueous solution after washing so that the itria concentration was 3 mol% to obtain a hydrated zirconia sol aqueous solution having an itria concentration of 3 mol%. An aqueous ammonia solution having a concentration of 0.1 mol / L was added to the hydrated zirconia sol aqueous solution to obtain a coprecipitate.

The obtained coprecipitate was filtered, washed with water, dried in the air at 120 ° C., and then calcinated in the air at 870 ° C. for 2 hours to obtain the zirconia powder of this example. The evaluation results of the obtained zirconia powder are shown in Table 1.

The obtained zirconia powder is premolded by a mold press, and then CIP-treated at a molding pressure of 200 MPa to obtain a molded product, which is then fired in the air at 900 ° C. for 2 hours to perform calcining of the present embodiment. I got a body. The evaluation results of the obtained calcined body are shown in Table 2, and the SEM observation diagram is shown in FIG.

Example 2
A zirconia powder was obtained in the same manner as in Example 1 except that the alumina sol was added to the hydrated zirconia sol aqueous solution so that the alumina concentration was 0.25% by weight.

A calcined product of this example was obtained by molding in the same manner as in Example 1 except that the zirconia powder was used.

The evaluation results of the zirconia powder of this example are shown in Table 1, the evaluation results of the zirconia calcined body are shown in Table 2, and the SEM observation diagram is shown in FIG.

Comparative Example 1
A hydrated zirconia sol aqueous solution was obtained in the same manner as in Example 1 except that an aqueous zirconium oxychloride solution having a zirconium concentration of 0.37 mol / L and a chloride ion concentration of 0.74 mol / L was used. The average sol particle size of the hydrated zirconia sol in the hydrated zirconia sol aqueous solution was 100 nm.

The obtained aqueous solution of hydrated zirconia sol was concentrated using an ultrafiltration membrane (molecular weight cut off: 6000). The unreacted zirconium content of the hydrated zirconia sol aqueous solution after concentration was 10% by weight.

Yttria chloride hexahydrate was added to the concentrated hydrated zirconia sol aqueous solution so that the yttria concentration was 3 mol% to obtain a hydrated zirconia sol aqueous solution having an yttria concentration of 3 mol%. The hydrated zirconia sol aqueous solution was spray-dried at a temperature of 180 ° C. The obtained dry powder was calcinated in the air at 1000 ° C. for 2 hours. After washing the obtained calcined powder with water, pure water is added to prepare a slurry having a concentration of 45%, alumina powder is added so that the alumina concentration becomes 0.25% by weight, and the mixture is pulverized with a vibration mill for 10 hours. To obtain zirconia powder. The evaluation results of the obtained zirconia powder are shown in Table 1.

A calcined product of this comparative example was obtained by molding and calcining in the same manner as in Example 1 except that the zirconia powder was used. The evaluation results of the obtained calcined body are shown in Table 2, and the SEM observation diagram is shown in FIG.

Comparative Example 2
Zirconia powder was obtained in the same manner as in Comparative Example 1 except that the dried powder was calcinated in the air at 1100 ° C. for 2 hours. The characteristics of the obtained zirconia powder are shown in Table 1.

A calcined product of this comparative example was obtained by molding and calcining in the same manner as in Example 1 except that the zirconia powder was used. The evaluation results of the obtained calcined body are shown in Table 2, and the SEM observation diagram is shown in FIG.

Comparative Example 3
Comparative Example 1 except that the dried powder was calcined in the air at 1150 ° C. for 2 hours, and the alumina powder was added so that the alumina concentration was 0.05% by weight and pulverized with a vibration mill for 30 hours. Zirconia powder was obtained in the same manner as in. The characteristics of the obtained zirconia powder are shown in Table 1.

A calcined product of this comparative example was obtained by molding and calcining in the same manner as in Example 1 except that the zirconia powder was used. The evaluation results of the obtained calcined body are shown in Table 2, and the SEM observation diagram is shown in FIG.

From Table 2, the calcined product of the example had a content ratio of coarse sintered particles of 0 particles / μm ² , and did not substantially contain coarse crystal particles. Further, as is clear from FIGS. 1 and 2, no particles having a maximum diameter of 0.5 μm or more were confirmed in the calcined body of this example.

Example 3
A zirconia calcined product was obtained in the same manner as in Example 1, and this was sintered in the air at 1350 ° C. for 2 hours to obtain a zirconia sintered body of this example. The evaluation results of the sintered body are shown in Table 3.

Example 4
The zirconia sintered body of this example was obtained by the same method as in Example 4 except that the zirconia calcined body obtained by the same method as in Example 2 was used. The evaluation results of the sintered body are shown in Table 3.

Comparative Example 4
A zirconia sintered body of this Comparative Example was obtained by the same method as in Example 4 except that the zirconia calcined body obtained by the same method as in Comparative Example 1 was used. The evaluation results of the sintered body are shown in Table 3.

Comparative Example 5
A zirconia sintered body of this Comparative Example was obtained by the same method as in Example 4 except that the zirconia calcined body obtained by the same method as in Comparative Example 1 was used. The evaluation results of the sintered body are shown in Table 3.

Comparative Example 6
A zirconia sintered body of this Comparative Example was obtained by the same method as in Example 4 except that the zirconia calcined body obtained by the same method as in Comparative Example 1 was used. The evaluation results of the sintered body are shown in Table 3.

The zirconia powder of the present invention can be used as a raw material for a zirconia sintered body, and can be used as a raw material for crusher members, precision machine parts, optical connector parts and other structural materials, dental materials and other biomaterials, decorative members and electronic device exteriors. It is useful as a raw material powder for exterior materials such as parts.

Claims (4)

A molding step of molding a zirconia powder in which the ratio of the particle size obtained by electron microscope observation to the particle size obtained from the BET specific surface area is 2.2 or more and 4.0 or less, and the obtained molded product is 800 ° C. or more and 1100. Zirconia tentatively having a firing step of firing at ° C. or lower, having a maximum diameter of 1 μm or more and a content ratio of 15 particles / μm ² or less and a density of 2.8 g / cm ³ or more and 3.6 g / cm ³ or less. How to make a roasted body. The production method according to claim 1, wherein the zirconia powder has a monoclinic crystal ratio of 10% or less. The production method according to claim 1 or 2, wherein the zirconia powder contains 2 mol% or more and 6 mol% yttria. The production method according to any one of claims 1 to 3, wherein the alumina content of the zirconia powder is 0% by weight or more and 0.3% by weight or less.

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